Carrier 38MGQ Series Service Manual page 55

P1(High pressure protection) error diagnosis and solution.
Error Code
Malfunction decision conditions
Supposed causes
Troubleshooting
P1
If the sampling voltage is not 5V, the LED displays the failure.
S
Wiring mistake
S
Over load protector faulty
S
System block
S
Outdoor PCB faulty
High pressure protec on
Whether the wiring
Whether the wiring
between the high pressure
between the high pressure
switch and main control
switch and main control
board is connected well or
board is connected well or
correctly
correctly
Yes
Whether the high
Whether the high
pressure protector
pressure protector
is broken
is broken
Method:
Disconnect the plug.
Method: Disconnect the plug.
Measure the resistance of the
the
Measure the resistance of
high pressure protector, if
high pressure protector, if
the protector is normal the
the protector is normal the
value is o,
value is o,
Yes
Check whether the outdoor
Check whether the outdoor
ambient temperature is
ambient temperature is
higher than 122 °F
higher than
No
Check if the outdoor unit
Check if the outdoor unit
l d
Yes
Check if the outdoor fan runs
Check if the outdoor fan runs
properly
properly
Yes
Check whether the heat
Check whether the heat
exchanger is dirty
exchanger is dirty
No
Replace outdoor main
Replace outdoor main
board
board
No
Check whether the refrigerant
Check whether the refrigerant
system is ok
system is ok
No
Connect it well
Connect it well
No
Replace high pressure protector
Replace high pressure protector
Yes Stop the unit
Stop the unit
NO
Make the outdoor unit ventilate well
Make the outdoor unit ventilate well
please ref
speed has been out of control
speed has been out of control
No
malf . Find out the cause and
have it solved.
have it solved.
Yes
Clean the heat exchanger
Clean the heat exchanger
55
f fan